Slow bursting activity in the cells in the hypothalamus of the mammalian brain is described, with a special emphasis on the vasopressinergic neurons of the supraoptic and paraventricular nuclei (SON/PVN). This patterned activity is compared to the one observed in the thalamic structure ? the intergeniculate leaflet of the lateral geniculate nucleus (IGL). Histograms of activity, bimodal distributions of the frequencies, averaged bursts and a few other characteristic properties of the oscillatory activity observed in SON/PVN and IGL are shown. Slow bursting activity of the intergeniculate leaflet cells is suggested to have a same function as has patterned firing of hypothalamic cells. Peptidergic contents of IGL cells, possibly attenuated blood-brain barrier in the area of this structure and its role in the adjustment of the circadian rhythms are some of the arguments to support this hypothesis.